Methods for cuttings for a wireline drilling tool

ABSTRACT

A method of removing cuttings from a workfront of a lateral borehole hole being drilled from a main borehole by a drilling tool is provided. The drilling tool comprising a tool body including a motor, an axial drive mechanism for advancing the tool body in the well, and a drill bit powered by the motor for drilling the underground formation at the workface and producing cuttings as the tool is advanced. The drilling tool is preferably connected to the surface by means of a cable extending through the lateral borehole and main borehole. The method independently comprising transporting the drilled cuttings from the workface to the part of the lateral borehole immediately behind the drilling tool. Transporting the drilled cuttings from immediately behind the drilling tool to the junction of the lateral borehole and the main well. And transporting the cuttings from the junction to a place of disposal.

TECHNICAL FIELD

This invention relates to methods for removing cuttings from a boreholebeing drilled with a wireline drilling tool. In particular, theinvention is applicable to the drilling of small boreholes in oil andgas wells and the like.

BACKGROUND ART

It has been proposed to drill lateral boreholes from a main boreholeusing a drilling tool that is conveyed and powered via a wireline cable.The aim of such a tool is to create lateral holes, from an alreadydrilled main wellbore. The laterals can have a range of dimensions, forexample an internal diameter of between <1 in to 4-6 in, and a length ofanything between 2-6 ft microperforations to 1000 ft mini multilaterals.They can be used, for example, to reach and produce bypassedhydrocarbon, to place an injection point to assist the displacement ofbypassed hydrocarbon, or to deploy sensors within the reservoir.

Small diameter holes can already be created using coiled tubingdrilling, but a wireline deployed system typically involves lessequipment at surface (in particular, no rig, or circulation system ofany kind may be needed) and hence costs can be reduced.

The rock cuttings generated in the hole-making process must be removed,in order to leave the lateral hole open for production or sensordeployment. The volume of a (2 inch×300 feet) hole is around 0.25 cubicmetres or 250 litres, and the associated mass of cuttings (assuming arock density of 2500 kg/cubic metre) is approximately 600 kg. Drillingrates can be of order 30-60 feet/hour. Hence, cuttings will be generatedat a mass rate of 60-120 kg/hour.

Dealing with the rock cuttings created during drilling is a criticalissue for success of the wireline conveyed technology. Whereas inconventional drilling there are separate down- and up-going fluid flowpaths (within drill pipe, and in the annulus outside between it and theformation) around which drilling mud can be circulated to carry thecuttings, with the wireline drilling tool there is only a single fluidfilled region in the hole behind the tool.

The object of the invention to provide methods by which the drilledcuttings can be transported out of the lateral borehole followingdrilling.

DISCLOSURE OF INVENTION

A first aspect of the invention provides a method of removing cuttingsfrom a workfront of a lateral borehole hole being drilled from a mainborehole by a drilling tool comprising a tool body including a motor, anaxial drive mechanism for advancing the tool body in the well, and adrill bit powered by the motor for drilling the underground formation atthe workface and producing cuttings as the tool is advanced, wherein thedrilling tool is connected to the surface by means of a cable extendingthrough the lateral borehole and main borehole, the method comprising:

-   -   transporting the drilled cuttings from the workface to the part        of the lateral borehole immediately behind the drilling tool;    -   transporting the drilled cuttings from immediately behind the        drilling tool to the junction of the lateral borehole and the        main well; and    -   transporting the cuttings from the junction to a place of        disposal;        wherein the transport around the drilling tool, transport from        the drilling tool to the junction and transport from the        junction to the place of disposal are all independent of each        other.

Preferably, the lateral borehole is filled with a fluid, at least partof which is circulated through the drilling tool during drilling. Inthis case, transport of the drilled cuttings past the drilling tool caninclude transport by local fluid circulation.

In another embodiment, the motion of the tool body can be used to movethe cuttings. One preferred embodiment of this is to provide the outersurface of the tool body with a thread formation (Archimedian screw) andto rotate the body to move the cuttings by the action of the thread.Other formations or appendages can be provided on the tool body andmoved to move the cuttings.

A still further embodiment comprises deformation of the tool body tocreate a peristaltic wave to move the cuttings.

Transport of the cuttings from behind the tool to the junction with themain borehole can include creating an asymmetric pulsatile flow,preferably with the drilling tool, in the lateral borehole to drive thecuttings to the junction.

In another embodiment, transport to the junction can be performed bydrilling the formation underbalanced so as to create a net flow of wellfluids back towards the main borehole.

In a still further embodiment, the tool body is provided with a tailpipe extending back along the lateral borehole, the cuttings beingtransported by pumping them along the tail pipe.

The cuttings can also be transported to the junction by withdrawing thedrilling tool from the lateral well so as to push the cuttings back tothe junction.

One or more separate transport devices can be provided between thedrilling tool and the junction which are shuttled back and forthcarrying the cuttings away from the drilling tool.

Flow back to the junction can also be created chemically, for example byigniting propellant charges behind the drilling tool.

Transport away from the junction can include allowing the cuttings tofall into a lower section of the main borehole. In one embodiment, thecuttings can be allowed to fall into a collector which is later removedfrom the well. In another, the cuttings are later cleaned out via atubing passed into the well from the surface. In a third, they aresimply left in the bottom of the hole.

BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS

FIG. 1 shows a schematic diagram of a wireline drilling system; and

FIG. 2 shows an embodiment of a shuttle device for cuttings disposal.

MODE(S) FOR CARRYING OUT THE INVENTION

This invention finds a particularly preferred application in wirelinedrilling systems which have been proposed for drilling lateral boreholesfrom a main well. FIG. 1 shows a schematic diagram of such a system,comprising a downhole drilling system 10 which is positioned in alateral well 12 extending from a main well 14. The downhole drillingsystem 10 is connected to the surface by means of a wireline cable 16which provides power and control signals during operation. The drillingsystem 10 comprises a BHA including a tractor system 18 for moving theBHA along the lateral well 12, a power and drive module 20 forconverting the electrical power provided by the cable 16 into mechanicaldrive for rotating a drill bit 22 and applying weight on bit duringdrilling.

During drilling a lateral hole, rock cuttings are created by the bit 22at the work front. These are typically a fine dust/powder due to the lowROP and high RPM used in these operations. These are then transportedout of the well in three stages:

-   1. From the workfront, past the drilling tool, to just behind the    tool;-   2. From behind the tool along the lateral to the junction with the    main hole;-   3. From the main-lateral junction to some place of ultimate    disposal.

There are various ways in which transport from the workfront past thedrilling tool might be achieved, including local fluid circulation,motion of the drilling tool body, deformation of the drilling tool bodyand the use of moveable appendages on the drilling tool body.

For a system based on local fluid circulation, fluid is drawn into thetool from the upper end (i.e. opposite to the drill bit 22), is pumpedto and through the drill bit, and returns carrying the cuttings alongthe annulus between tool and formation. Systems based on motion of thedrilling tool body can take a number of forms e.g., the tool bodyrotates, and a screw thread on the outside forces the cuttingsbackwards. In another system, the surface of the tool body deforms so ascreate a peristaltic wave which forces the cuttings backwards. Moveableappendages (scrapers, hairs or cilia, fins or claws) can be provided onthe surface of the tool to grasp and push the cuttings backwards orgenerate a fluid flow that has that effect.

Transport from the junction between the lateral well and the main wellcan involve simply dumping the cuttings into an extended rat-holesection of the main well, dumping into the rat-hole and cleaning outlater with coiled tubing, or dropping them into a junk basket which islater lifted to surface using slickline.

It is beneficial to minimize the volume of cuttings to be transportedover large distances. There are a number of possible ways of doing this.When drilling carbonate reservoirs, the drilling fluid can be acidic, soas to dissolve the cuttings. The chemical properties of the drillingfluid can be modified by energy input (e.g. in electrical form) at thedrilling tool, so as to ensure that aggressive chemical conditions areonly present where they are needed and not throughout the hole wherethey might cause damage to the drilling tool itself. The wellbore fluidcontaining the dissolved rock is flowed out of the hole when it is puton production. As an alternative to complete dissolution, the cuttingscan be ground to colloidal size, so that they remain in suspension underthe action of Brownian motion (the wellbore fluids should be tailoredchemically so as to stabilize this suspension against flocculation andaggregation of the suspended solids).

Some fraction of the drilled cuttings can be compacted and plasteredinto the wellbore wall. While for production holes formation damage andcreation of a filter cake is not desirable, for injectors, or holes forsensor placement, the hydraulic sealing that this would create may benecessary. The cuttings can also be compacted, so as to eliminate thevolume of the porosity. Other approaches to cuttings disposal creating afracture in the wellbore wall, and pumping them into that newly createdvolume; or an initially non-circular and over-gauge hole can be drilled,and some cuttings compacted onto the hole wall so as to created a finalcircular hole of the required gauge diameter.

There are a number of approaches to providing transport from behind thetool along the lateral to the junction with the main.

One approach is to use an asymmetric pulsatile flow. This involves, forexample, sucking wellbore fluids slowly into a reservoir within thedrilling tool, then expelling them quickly so as to blow the cuttingsback along hole. This is a hydraulic transport mechanism, which exploitsthe non-linear rate dependence of most hydrodynamic processes togenerate a mean solids flow backward along the hole. In order to ensuregood transport, it may be necessary to combine with a large amplitudezero mean pulsatile flow (or acoustic field) to prevent the cuttingsfrom becoming packed in a bed on the low side of the hole. Theproperties of the fluid filling the hole are also important, and shouldbe chosen so as to avoid stickiness and/or aggregation of the cuttings.It may also be beneficial here, or elsewhere, to pre-process thecuttings into a shape and size that is optimal for transport.

Drilling underbalanced is another way to convey the cuttings to thejunction with the main well. In productive zones, drilling underbalancedwill cause fluids to flow into the lateral. The resulting axial flowwill transport the cuttings along the hole, and the radial inflow willcontribute to lifting and fluidizing the cuttings bed. Controlledunderbalance can be generated using a gas lift valve deployed at ashallow depth. Other benefits of drilling underbalanced are well-known,and include reduced risk of sticking and formation damage, and increasedrate of penetration. The underbalance can be applied continuously, or inpulses so as to create a short period of intense flow (again, thenon-linearity of most hydraulic transport processes means that shortperiods of high velocity will be more effective that continuous low rateflow, for the same time-mean rate). In designing the specific process tobe allied, a balance must be achieved between volume of cuttings to bemoved and the ability of the formation to supply fluid.

The cuttings can be pumped back along the lateral in a tail pipe. Thedrilling tool trails alight weight tail pipe, along which cuttings arepumped. Fluid and cuttings are drawn in, at the drill bit, and are thenpumped backwards through the tool and into the tail pipe. The interiorprofile of the tail pipe can be tailored so as to enhance transport,e.g. a helical “swirl pipe” profile, or periodic baffles orconstrictions, all of which can assist conveyance at low fluidvelocities, and may induce turbulent flow, which will enhance (fine)cuttings carrying capabilities.

The drilling tool itself can be used to move the cuttings. In this case,cuttings are allowed to build up behind the working drilling tool.Periodically drilling is stopped and the tool is pulled back along thelateral, so that the accumulated cuttings are pushed along in front ofthe tool (in this case pushed by the upper end of the tool).

A number of techniques are based on the idea of shuttles. The basic ideais to move the cuttings by carrying or pushing them using a separatevehicle that shuttles back and forth between the drilling tool and thelateral-main junction. Many realizations are possible. The vehicle can,for example, pull itself along the wireline, or move using wheels,tracks, or feet contacting the hole wall. It can carry its own powersupply (recharged at the drilling tool, or at a mother tool in the mainhole), or gather power inductively from the wireline cable, or it can bepassive and moved by winching from the drilling tool and/or a tool atthe junction. Single or multiple vehicles can be used. Examples include:

-   -   a robot shuttle “bulldozer”, pushing cuttings before it;    -   compacting cuttings into spheres and rolling them back, using        the bulldozer, in line along the lateral;    -   compacting or encapsulating the cuttings into large well defined        “beads”, and pushing them back along the wireline cable as if on        a necklace, removing them at surface on pulling out of hole or        dropping them into the junk basket or rat hole;    -   a robot shuttle “dumper truck”, carrying cuttings; and    -   a “jawed” shuttle that runs in along hole, drives jaws into        cuttings pile behind tool, closes jaws so as to pick up a volume        of cuttings and reverses back along lateral to drop cuttings at        junction.

There are various possibilities for implementation of an autonomousvehicle to carry out these tasks. FIG. 2 shows an embodiment of the‘jawed’ shuttle which comprises a shuttle body 30 which is attached tothe wireline cable 16 connected to the drilling tool 10. The shuttlebody includes a tractor device 32 which can be operated to move theshuttle back and forth along the cable 16. A pair of jaws 34 areprovided at the end of the body 30 and can be moved between openpositions in which the interior of the shuttle communicates with theborehole, and a closed position in which it is obscured. In FIG. 2, thejaws 34 are shown in the open position. In use, the shuttle can start atone end of the lateral well, for example close to the junction with themain well (not shown). The jaws 34 can then be opened and the tractordevice 32 activated to draw the shuttle along the cable 16. The jaws 34dig into the cuttings bed 36 (typically on the lower side of thelateral) and the motion of the shuttle scoops the cuttings into theshuttle body 30. When the body is full, the tractor device can beoperated to withdraw the shuttle to another location where the storedcuttings can be disposed of. This process can be repeated while drillingproceeds.

Another approach is to use techniques based on a distributed actuationconcept. In this case, the basic idea is to distribute the motive forcesalong the entire length of the lateral, for example by using cilia onthe wireline, a peristaltic sheath surrounding wireline, an Archimedesscrew surrounding wireline, an Archimedes screw in a tail pipe, drivenfrom tool. In other cases, the techniques mimic leaf-cutter ants througha swarm of tiny carrying devices each of which carries a small load, ora chain of people passing fire buckets along the line.

Chemical techniques can be used to create extra flow. The drilling toolcan contain a number of charges of propellant, that are ignitedperiodically. A large volume of gas is generated, which causes a flowalong the lateral, which in turn carries the cuttings.

It is also possible to tailor the hole trajectory to assist transport.This can involve drilling the hole slightly uphill, and allowing thecuttings to fall downhill under gravity, optionally with shaking, orpulse flow, to assist transport, or use continuous direction/azimuth andinclination measurements to ensure that the borehole has minimaltortuosity to minimize potential cleaning hazards, e.g., sumps, etc.

Other changes within the scope of the patent will be apparent.

1. A method of removing cuttings from a workfront of a lateral boreholehole being drilled from a main borehole by a drilling tool comprising atool body including a motor, an axial drive mechanism for advancing thetool body in the well, and a drill bit powered by the motor for drillingthe underground formation at the workface and producing cuttings as thetool is advanced, wherein the drilling tool is connected to the surfaceand powered by means of a cable extending through the lateral boreholeand main borehole, the method comprising: transporting the drilledcuttings from the workface to the part of the lateral boreholeimmediately behind the drilling tool; transporting the drilled cuttingsfrom immediately behind the drilling tool to the junction of the lateralborehole and the main well; and transporting the cuttings from thejunction to a place of disposal; wherein the steps of transportingaround the drilling tool, transporting from the drilling tool to thejunction and transporting from the junction to the place of disposal areall independent of each other.
 2. A method as claimed in claim 1,wherein the lateral borehole is filled with a fluid, at least part ofwhich is circulated through the drilling tool during drilling.
 3. Amethod as claimed in claim 2, wherein transport of the drilled cuttingspast or through the drilling tool includes transport by local fluidcirculation.
 4. A method as claimed in claim 1, wherein the motion ofthe tool body is used to move the cuttings.
 5. A method as claimed inclaim 4, comprising providing the outer surface of the tool body with athread formation and rotating the body to move the cuttings by theaction of the thread.
 6. A method as claimed in claim 4, wherein otherformations or appendages are provided on the tool body and moved to movethe cuttings.
 7. A method as claimed in claim 4, comprising deformingthe tool body to create a peristaltic wave to move the cuttings.
 8. Amethod as claimed in claim 1, wherein transport of the cuttings frombehind the tool to the junction with the main borehole includes creatingan asymmetric pulsatile flow in the lateral borehole to drive thecuttings to the junction.
 9. A method as claimed in claim 8, wherein thepulsatile flow is created using the drilling tool.
 10. A method asclaimed in claim 1, wherein transport to the junction is performed bydrilling the formation underbalanced so as to create a net flow of wellfluids back towards the main borehole.
 11. A method as claimed in claim10, wherein the underbalance is created by a periodic burst of gas thatallows the overall rockface pressure to be maintained at over or nearbalance, but helps increase transport velocities in the borehole.
 12. Amethod as claimed in claim 1, wherein the tool body is provided with atail pipe extending back along the lateral borehole, the cuttings beingtransported by pumping them along the tail pipe.
 13. A method as claimedin claim 1, wherein cuttings are transported to the, junction bywithdrawing the drilling tool from the lateral well so as to push thecuttings back to the junction.
 14. A method as claimed in claim 1,wherein one or more separate transport devices are provided between thedrilling tool and the junction which are shuttled back and forthcarrying the cuttings away from the drilling tool.
 15. A method asclaimed in claim 1, wherein flow back to the junction is createdchemically
 16. A method as claimed in claim 15, wherein flow is createdby igniting propellant charges behind the drilling tool.
 17. A method asclaimed in claim 1, wherein transport away from the junction includesallowing the cuttings to fall into a lower section of the main borehole.18. A method as claimed in claim 17, wherein the cuttings are allowed tofall into a collector which is later removed from the well.
 19. A methodas claimed in claim 17, wherein the cuttings are later cleaned out via asecondary or plurality of tubing(s) passed into the well from thesurface.